In one aspect, the invention relates to a heat exchanger. In another aspect, the invention relates to recuperating heat from a combustion gas stream. In yet another aspect, the invention relates to maintenance of a good heat exchange relationship. In yet another aspect, the invention relates to improved operation of a heat exchanger.
Heat exchangers are commonly deployed for steam generation services. One type of such service utilizes indirect heat exchange between water and combustion gases to convert the water into steam. Shell and tube heat exchangers are very popular for this application.
A common problem encountered in generating steam from combustion gases is that deposits reduce the efficiency of heat exchange. The deposits can occur on the steam side of the heat exchanger or on the combustion gas side. The deposits on the water side of the heat exchanger can be extremely severe where the water to be converted to steam has a high solids content, but excessive deposits can frequently be controlled by periodically blowing down the heat exchanger. Deposits on the combustion gas side of the heat exchanger can be more difficult to control. One type of combustion gas stream which leaves profuse deposits is the off-gas stream from a carbon black reactor. The particulate load in such a stream can be measured in terms of pounds per thousand standard cubic feet of gases. The particles with which the gases are laden are very fine. The thermophoretic force between the hot particulates and the relatively cool boiler tube wall drives the particulates to deposit on the wall. The result is a significant decrease in heat transfer coefficient and a low boiler efficiency. A heat exchange apparatus and process which resists fouling would be very desirable, especially for this application.